The 1950 Central Scientific Company catalogue has rather an
extensive history of this apparatus, which is designed to show the relationship
between the force exerted by a stream of water and its rate of flow.

The original suggestion was made by Reichel in 1891, and it
was repeated by Coleman, writing in School Science and Mathematics
in 1912.

A jet of water of known ` area strikes a plate on the end
of the pendulum that is pivoted at the top of the apparatus. A weight hung
from the horizontal beam supplies a torque that balances the torque exerted
by the stream of water. The spent water is collected for a known period
of time, and the momentum delivered per unit time can be calculated and
compared to the force needed to balance the system.

The apparatus is at Kenyon College. In 1940 it cost $22; by
1950 the cost had risen to $60.